In recent years, in the field of Si (silicon) photonics, it is reported that light from an SMF (single mode fiber) is guided into an Si waveguide via the coupling by use of a grating coupler, and then received by a waveguide-based PD (photodetector). Utilizing a grating coupler enables optical path conversion and the coupling into a waveguide; however, an SMF is required as input elements for coupling with a single-mode waveguide. Note that an example of this type of an optical receiver is disclosed in non-patent-related document 2, where a TE mode and a TM mode are separated from each other by use of a two-dimensional grating, thereby coupling the two modes with a PD.
Meanwhile, a surface-type detector comprising Ge (Germanium) is also reported in the field of Si photonics.
In optical interconnection, an MMF (multimode fiber), which has a large core-diameter, is used for realizing low-cost optical transmission. Compared to an SMF, an MMF provides larger assembly tolerance with respect to a light source, thus reducing of costs can be realized. Meanwhile, in order for a PD to receive light from an MMF at low costs, a surface-type detector having a large light-receiving area is used.